US3781105A - Constant current biasing transfer system - Google Patents

Constant current biasing transfer system Download PDF

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US3781105A
US3781105A US00309562A US3781105DA US3781105A US 3781105 A US3781105 A US 3781105A US 00309562 A US00309562 A US 00309562A US 3781105D A US3781105D A US 3781105DA US 3781105 A US3781105 A US 3781105A
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transfer
nip
roller
electrode
electrical
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T Meagher
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Xerox Corp
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Xerox Corp
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G15/00—Apparatus for electrographic processes using a charge pattern
    • G03G15/14—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base
    • G03G15/16—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer
    • G03G15/1665—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer by introducing the second base in the nip formed by the recording member and at least one transfer member, e.g. in combination with bias or heat
    • G03G15/167—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer by introducing the second base in the nip formed by the recording member and at least one transfer member, e.g. in combination with bias or heat at least one of the recording member or the transfer member being rotatable during the transfer
    • G03G15/1675—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer by introducing the second base in the nip formed by the recording member and at least one transfer member, e.g. in combination with bias or heat at least one of the recording member or the transfer member being rotatable during the transfer with means for controlling the bias applied in the transfer nip

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  • PAIENIEB HECZS I973 SHEET 4 BF 4 SOURCE CONSTANT CURRENT lBIASlNG TRANSFER SYSTEM BACKGROUND OF THE INVENTION This invention relates to the transfer of electrically charged particles between supports. Specifically, this invention relates to methods and apparatus for the improved electrostatic transfer of xerographic toner particles with electric fields established by roller or endless belt electrodes.
  • Roller electrode transfer systems employ D.C. electric fields to move charged particles such as xerographic toner from first to second supporting surfaces. (By D.C. it is meant that the direction of the field vectors are not reversed 180 on a unit time basis.) The purpose is to exert an electrical force on the charged particles that moves them from the first to the second support.
  • the electrodes establishing the transfer field generally include a roller electrode and a backing electrode.
  • the .backing electrode is one adjacent the support initially carrying the particles.
  • the backing electrode is often in the configuration of either a flat plate or a cylinder, and is supported for movement relative to the roller electrode.
  • the region of closest proximity between the two electrodes defines a nip region between which passes the second, or final, particle support or transfer member.
  • the geometry of the various apparatus of roller transfer systems is symmetrical.
  • the initial particle support may be a conductive member and thereby comprise the backing electrode.
  • the initial support may be, for example, an insulator, a photosensitive semiconductor, or have an insulative substrate, at least in a link or web positioned between the two electrodes, and may carry charges affecting the transfer field.
  • the transfer of toner images between supporting surfaces is accomplished with the electrostatic transfer of either a corotron or a roller electrode biased to constant potential (constant voltage) levels.
  • a corotron or roller transfer systems Various trade-offs are made in choosing between the corotron or roller transfer systems.
  • the corotron system is particularly noted for its relative simplicity, but the charges deposited by the corotron electrostatically tack the transfer support (e.g., paper) to the original toner support (e.g., a photoconductor) in addition to creating the desired electric field effecting transfer of the toner to the paper.
  • This strong (tacking) attraction between the paper and the original toner support makes it mechanically difficult to separate or detack the two supports.
  • the detack problem is less severe when the transfer member is a web or other mechanically gripped memher, and for that reason web transfer members have been generally felt to be better suited for higher speed copying machines, and for biased roller transfer systems. No commercially successful copying machine is believed to have employed a roller transfer system with cut sheet transfer members.
  • corotron is a voltage sensitive device that provides a current proportional to the potential difference between it and the surface from which it is spaced, by the generation of a corona with ion flow toward the surface.
  • Current control is usually not a problem.
  • corotron current control when needed, may be accomplished by operating well above some minimum current level with a total current (largely to the shield) which is high and relatively constant.
  • variable current sources are believed in the art to be nreferred in applications where the objective is the charging of a non-uniformly charged surface to a more uniform potential.
  • a photoconductor bearing an electrical image into a transfer area is such a non-uniformly charged surface.
  • roller transfer systems rely upon some minimum voltage difference between the bias roller electrode and the photoconductor (or other initial toner support) to transfer the charged toner particles to the paper.
  • some, but excessive, charging of the sheet of paper is highly desirable within the post-nip region to keep the transferred toner particles tacked to the paper after the paper has left the region of high field around the nip formed between the roller and paper.
  • This corona charging can be provided in thepresent invention by the selective ionization of air at the nip exit region.
  • constant current control of the bias voltage supply in a transfer roller system as disclosed herein rather than constant voltage control, provides a highly desirable and novel result. It can provide a controlled amount of desired post-nip corona with suppressed prenip corona over a wide range of physical variations in operating conditions, including substantial relative humidity changes.
  • Another object of the present invention is to enhance xerographic imaging systems by maintaining constant corona currents to members being charged in a biased member transfer system.
  • Yet another object of the invention is to reliably control the pre-nip and post-nip corona currents generated in a roller electrode system over a wide range of humidity and equipment variations.
  • the present transfer system is capable of handling a wide range of transfer members wherein pre-nip and post-nip corona currents are effectively regulated, including cut sheets.
  • FIG. 1 is a schematic elevational side view of an exemplary biased roller electrode transfer system in accordance with the present invention.
  • FIG. 2 is a schematic of one example of an electrical circuit capable of serving as the constant current energy source for the present transfer system.
  • FIG. 3 is a graphof electrical field as a function of time (where the center of the transfer roller nip is time) in three regions: at the'nip entrance (pre-nip); in the nip; and after the nip (post-nip).
  • FIG. 4 is a graph comparing the applied bias to an exemplary transfer roll versus roll resistivity and relative humidity.
  • FIG. 5 is a graph comparing nip fields versus roll resi'stivities for an exemplary roll.
  • FIG. 6 is'a schematic cross-sectional side view of another biased roller, transfer sheet, and photoconductor (or other insulating surface) illustrating the post-nip ionization of air around the roller during the transfer process and the relaxation and self-leveling abilities of the transfer roller.
  • I DETAILED DESCRIPTION -Xerographic toner l0 typically comprises microscopic size particles (0.1 microns) that are opaque or include opaque materials. Electrically, the toner is highly insulating and carries a net electrical charge. The desired polarity of the toner charge depends on the polarity scheme of the imaging system. In the presently described embodiment the toner is assumed to have a net negative charge,vwhich thereby suggests the other polarities illustrated, discussed and intimated. Quite clearly, alternative system based on positively charged toner particles are also benefited by the present invention, although a detaileddescription thereof is omitted here, as it would be redundant.
  • the photoconductor (photoreceptor) 11 is, for the purposes of the present discussion, a moving electrical insulator'web. It is supported by a conductive core (roller) 12 which is electrically coupled here to a ground potential 13 as a convenient and safe potential level.
  • the backing electrode may also be a continuous conductive backing layer of the photoreceptor belt, grounded by a contacting grounded wiper, in which case the backing roller 12 can be non-conductive.
  • the transfer roller should not be allowed to contact any grounded surface during operation.
  • the plus signs 14 on the photoconductor 11 represents positive charges associated with an electrical latent image on it.
  • the latent image is a pattern of charge 14 created by steps including uniformly charging the photoreceptor and then exposing it to a light image.
  • the latent electrical image may' .be created even on a nonphotosensitive insulator by selectively depositing charge on the insulator through a stencil shaped in the form of an image, or other imaging means.
  • the latent electrical image is developed by steps including bringing toner particles 10 adjacent the latent images. The fields associated with charge 14 then electrostatically tack the charged toner particles to the insulator l1.
  • the transfer of the toner to a transfer member can be accomplished electrostatically by a roller electrode, as illustrated in Fitch U. S. Pat. No. 2,807,233, or by a corotron as described in Shaffert U. S. Pat. No. 2,576,047.
  • the bias supplied to the transfer device is indicated as a constant voltage energy source.
  • the present transfer system uses a novel transfer roller biasing scheme to greatly enhance the electrostatic transfer operation.
  • a transfer roller 15 is appropriately journaled for rotation at an angular velocity such that the peripheral speed of the roller is substantially equal to the speed of the insulator 11.
  • the arrows shown indicate the relative direction of movement for the roller 15, insulator 11 and paper 16.
  • pre-nip and post-nip used herein refer to the direction of travel of the transfer sheet 16 through the nip, and in FIG. 6 correspond to the right and left hand regions respectively adjacent the nip l7.
  • the exemplary roller 15 here includes an electrically selfleveling outer layer 20, an electrically relaxable next (inner) layer 21 and a central conductive core or axle 22.
  • the constant current electrical bias or energy source 23 is electrically connected to the conductive core 22.
  • the heart of the roller electrode 15 is the thick relaxable layer 21, which has a bulk resistivity falling in a well defined operating range selected in relation to roll diameter and surface velocity.
  • the bulk resistivity of the relaxable layer can vary over the range from about 10 to about l0 ohms per centimeter.
  • the preferred resistivity ranges may varyfor transfer systems designed to operate at different throughput speeds of the transfer sheet 16.
  • roller 15 diameter of about 3 inches
  • roller 12 diameter of about 5 inches
  • paper speed of from about 10 to about 20 inches per second.
  • a properly selected resistivity range is critical for the relaxable layer 21 operation, even for present day copying speeds of 10 to 20 inches per second. (Doubling the speed is generally equivalent to halving the resistivity).
  • the relatively soft, thick, electrically relaxable body 21 may be mounted directly on the axle 22 of the bias roll.
  • the relatively low durometer of this material allows good mechanical contact in the transfer zone at moderate pressures and eliminates hollow character" transfer under normal operating conditions. Since the relaxation time of the core material is long compared to the ion transfer time of gaseous discharges, during air breakdown the roll acts like an insulator, protects against arcing and helps control the amount of charge transferred at any point on the surface.
  • the relaxable layer 21 comprises a material that functionally takes a selected time period to transmit a charge from the conductive core 22 to the interface 47 between the relaxable layer 21 and the self-leveling layer 20 sufficient to restore said interface 47 to about the bias potential applied to the core 22.
  • This selected time period is that corresponding to the roller surface speed and nip region width, i.e., roughly greater than the time any point on the transfer roller is in the nip region, and is chosen to be approximately one quarter of the roller revolution time. Functionally, this means that the magnitude of the external electric field increases significantly from the pre-nip entrance toward the postnip exit, while the field within the relaxable layer diminishes.
  • a relaxable layer is one that has an external voltage profile which is non-symmetrical about the transfer nip.
  • the ideal conditions are to have a field strength below that for substantial air ionization in the air gap at the entrance to the nip, and a field strength above that required for air ionization in the air gap just beyond the exit of the nip. [Some pre-nip ionization may be allowable].
  • the present invention realizes these goals.
  • the (outer) self-leveling layer 20 is a leaky insulator.
  • the layer 20 is selected for substantially higher resistive values, which in the present embodiments means in the order of about to 10 ohms per centimeter.
  • the self-leveling layer includes materials, (or is so related to the relaxable layer), such that charges applied to the outer surface 24 of the selfleveling layer will be generally dissipated'within one revolution of the roller 15. This dissipation of charge is desirable to prevent suppression of the transfer field in the nip.
  • the self-leveling layer 20 thickness divided by its dielectric constant should be substantially greater than any other material in the nip in order for its capacitance to be much less than such other materials, as desired.
  • the self-leveling layer 20 also acts as a thin insulating layer coated on the surface of the relaxable core material to help protect the roll during air breakdown, to act as a moisture barrier, to limit current flow through the roll, and to make the roll surface easy to clean.
  • the relaxable material is durable and cleanable the self-leveling layer 20 is not essential.
  • a constant current supply can compensate for nonleveling as long as the voltage buildup across this layer 20 does not cause the power supply to exceed its rated maximum output voltage, and as long as the charge on this layer is reasonably uniform. Some non-leveling is tolerable.
  • the paper or other transfer sheet 16 is here a. cut sheet (versus a web) that is fed into and extracted from the transfer system by conventional or appropriate means.
  • a cut sheet versus a web
  • FIG. 1 One example is illustrated in FIG. 1 and discussed in more detail later.
  • the comparison of the sheet to the web isintended to differentiate sheet 16 from those transfer members that are guided through the transfer system by being mechanically coupled to the transfer roller, as illustrated in the above-cited Dolcimascolo et al. patent, or wound between spools or the like as illustrated in the Fitch patent, supra.
  • the transfer sheet typically will be conventional 20 pound bond paper with or without a plastic coating. It should be understood, however, that an advantage of the present system is that it can operate with paper weights ranging from nine pound vellum" to pound or greater card stock. Alternately, the transfer sheet here may include various transparent materials, such as polyester resin sheet sold commercially under the trade name Mylar.
  • paper is generally a fair insulator at low RH and a fair conductor at high RH. Consequently, the charge illustrated by the plus signs 30 on the non-image side of the transfer sheet 16 may actually leak onto the image side of the sheet if the sheet is reasonably conductive.
  • the plastics are, of course, generally always highly insulating.
  • a key factor in the improved operation of the present transfer system is the constant current energy (bias) source 23. Its automatic current control controls prenip ionization to tolerable levels while allowing a desired amount of post-nip ionization even when RH variations, roller material aging, paper thickness changes, and other factors change the electrical parameters of the transfer system, and yet while maintaining high transfer fields.
  • bias circuit 23 Before the bias circuit 23 is described here, however, it is helpful to first discuss the electric fields holding the toner to its support and the roles the relaxable and self-leveling layers of roller 15 play in the transfer process.
  • the toner 10 While the toner 10 is carried by the insulator 11 toward the nip region 17, the toner is tacked to the insulator by the fields associated with the latent image charge 14 and by other adhesive forces such as VanderWaal forces.
  • the charge 14 may be substantially altered before reaching the nip, as in systems where a photoconductor is involved, by exposing the photoconductor to light discharge.
  • the original support is still able to retain the toner particles in place with such reduced field strengths.
  • the reduced tacking fields are advantageous for the simple reason that transfer can occur with a lower nip field. Another reason is that if charge 14 is not reduced, excessive fields prior to entering the nip might cause air ionization, or cause fuzzy images (or loss in sharpness) due to premature transfer of the toner while the gap is too large. It is to be noted, however, that the present transfer system is effective whether or not the latent image, e.g., charge 14, is altered prior to transfer. One reason for this is that it is considered that the constant current bias 23 may offset the bad effects that excessive image charge 14 may otherwise have on the transfer operation.
  • the pre-transfer illumination of the photoconductor is desirable because it insures that the transfer current density in image regions is nearly equal to the current density in background regions. Without it the current density in background regions would be much larger than in image regions, particularly with low resistivity bias rolls, thus reducing transfer efficiency.
  • roller 15 may be explained in connection with the generalized curves in FIG. 3.
  • the time scale along the horizontal axis represents the movement of the transfer sheet 16 through the nip region.
  • the pre-nip period is to the left of the nip period 43,
  • the horizontal axis also corresponds to path distances from the nip area 17.
  • the volts-per-micron scale along the vertical axis of FIG. 3 represents relative transfer field intensity along the path of the transfer sheet.
  • the field observed is that between the outer surface 24 of the roller and the free surface of the toner support 11. It is that field which effects the transfer of the toner 10 between supports 11 and 16.
  • Curve 40 in FIG. 3 is the Paschen curve which represents the field intensities at or above which ionization of air will normally occur (on both sides of the nip).
  • Curve 41 is the field curve generated by the roller transfer system of FIGS. 1 and 6.
  • Curve 42 is an exemplary curve for prior art rollers not having a relaxable layer 21, e.g., conductive rollers and conductive rollers overcoated with high resistance and/or high dielectric materials. This curve 42' is included to comparatively dramatize the desirable asymmetrical nature of the subject curve 41, which permits post-nip but prevents prenip ionization of air.
  • Curve 42 represents the prior approach to roller transfer in that it is symmetrical about the nip contact region (represented by' the time period 43) in the absence of toner and air ionization effects.
  • Curve 41 is asymmetrical because of the effects of the relaxable and self-leveling layers during and just after exit from the nip region 43.
  • the object is to have portion 41B of the curve 41 continue upward in post-nip until the Paschen curve is reached, thereby initiating the desired post-nip corona ionization.
  • pre-nip portion 41A is selected to remain below the Paschen curve 40 to realize the preferred condition of no pre-nip ionization.
  • the transfer conditions depicted by FIG. 3 is schematically illustrated by the plus signs 48 in FIG. 6.
  • the nlus signs 48 represent charge at the roller internal interface 47.
  • the relaxable layer 21 Prior to entering the nip, the relaxable layer 21 is not subjected to high, internal fields; thatis, its outer surface is at substantially the same potential as the core 22.
  • the roller surface Just prior to and in the nip area the roller surface becomes closely spaced from the grounded backing electrode (support) 12. This tends to draw charge toward the roller 15 surface, but charge movement is resisted by the roller resistivity.
  • the charge density at interface 47 increases as the relaxable layer proceeds through the nip in proportion to the resistivity of the relaxable layer.
  • the charge density will generally continue to increase due to the internal field in the relaxable layer 21, or.the induced charge may have nearly reached equalibrium; in either case the rapid increase in the air gap soon after separation occurs causes the ionization level to be reached for the field strength corresponding to the residual charge density.
  • the plus signs 30 and negative signs 49 represent positive and negative ions deposited on the transfer sheet 16 and the outer surface 24 of the roller 15, respectively, as a result of the post-nip ionization of the air in the gap.
  • a plus sign 48 is positioned at interface 47 opposite each negative sign 49 to represent an induced counter-charge within the roller which was brought to interface 47 during relaxation of material 21 in the nip.
  • the positive charge 30 holds (and continues to maintain) the transferred toner 10 to sheet 16.
  • the negative charge 49 is dissipated by current flow through the self-leveling layer 20 during the subsequent one to five revolutions of the roller.
  • constant current biasing is the method and means for keeping curve portion 41A below the Paschen curve 40 to prevent prenip ionization and for insuring that curve portion 41B intersects the Paschen curve in the post-nip region.
  • Curves 54, 55, and 56 in FIG. 4 depict the beneficial operation of constant current biasing.
  • Curves 54 and 56 represent the field levels for pre-nip and post-nip ionization, respectively, versus changes in the resistivity of roller 15 for the previously defined resistivity range.
  • the roller resistivity variations are exemplary changes in the resistivity of the relaxable layer with changes in RH.
  • Curve 55 which lies in the ideal region between curves 54 and 56, is obtained by keeping the roller current constant.
  • Curves 60 and 61 in FIG. illustrate a family of curves for constant current that permit field intensities below the pre-nip ionization level.
  • Curve 62 represents the pre-nip ionization level for the resistance range shown.
  • the current referred to as being held constant throughout this description is the current to the roller core 23, I
  • This roller current I is, by reason of conservation of charge, basically equal to the post-nip ionization current I (Substantially zero pre-nip current is, of course, one of the desired operating conditions here.)
  • the constant current bias source 23 may be described as a device for automatically widely varying the potential level coupled to roller 15 to automatically compensate for I changes, due to the connected load (resistance) changes, which are due to changes in ambient RH and temperature and aging of materials plus other factors tending to effect the pre-nip, nip and post-nip field levels such as paper thickness, charge build-up on the self-leveling layer, etc.
  • the constant current source output I is equal to about 1.5 microamps per inch, where the inch refers to the length of the roller along its axis (perpendicular to the plane of FIG. 6).
  • the wide internal roller resistivity swing previously discussed requires the bias potential on core 22 here to vary from about 800 to about 4,000 volts to maintain this constant current of 1.5 microamps per inch (Note FIG. 4).
  • the bias source 23 output voltage must vary automatically over this voltage range.
  • the air gaps W, X, Y and Z (FIG; 6) around roller 15, sheet 16 and support 11 are important.
  • the paper transfer sheets with which this invention is particularly concerned will necessarily involve such various air gaps although possibly in some altered manner from that illustrated.
  • gaps W and X cause no particular electrical problem to the transfer operation and the relation of gaps W and X to each other is not particularly critical.
  • Pre-nip ionization in gap W results in charging of the sheet 16 which in turn may cuase premature toner transfer resulting in poor image resolution. It also induces ionization in gap X. Ionization in gap X causes the charge associated with toner 10 to be altered.
  • Pre-nip ionization effects will be less if X is smaller than W, i.e., if the paner is closest to the photoconductor. High fields in gap X can also cause the toner to jump prematurely across the air gap W.
  • Air gaps Y and Z are critical because the desired post-nip ionization must occur in gap Y.
  • the ionization in gap Y enables the charge 30 of appropriate sign to tack the transferred toner to sheet 16. (However, as noted, it also tacks the sheet 16 to the photoconductor ll.)
  • Ionization, if any, in gap Z usually follows that in gap Y and reduces the net charge in the paper and adds to the negative charge associated with the transferred toner l0, bonding it more strongly to the paper.
  • Ionization in gap Z before gap Y would lead to a negative charge on the paper and untacked toner.
  • Ionization in gap Y in preference to gap Z, and efficient transfer prior to stripping is insured by making gap Y open at a faster rate than, and prior to, gap Z. This is accomplished respectively in the present embodiment by selecting the radius of roller surface 24 to be less (e.g, by a factor of 2 4 times) than the radius of support 11, and by the partial wrap in post-nip of the sheet 16 and support 11 together on the backing roller 12. Le, stripping occurs substantially after the transfer nip.
  • the radius of support 11 is established for the apparatus of FIG. 6 by the radius of the backing roller 12.
  • the shape of the Paschen curve for an air gap can be affected by the paper position.
  • X and W air ionization will require a higher field level than for a single gap, as Y (which is desired here.)
  • the exemplary electrical circuit shown in FIG. 2 is capable of providing the constant current biasing voltage source 23 for roller 15.
  • Transistors 0301 and 0302 level out input power E,-,, to a transformer T1 primary. Initially assume the circuit is working in a steady state condition, supplying current I within the abovediscussed specifications to the load (core 22). If the load resistance suddenly increases (e.g., when paper is fed between the bias roller and photoreceptor), the load current tends to decrease from its steady state value.
  • a load current sensing return path is provided up through zener CR308, current setting pot R8 and resistance R312 and then to the transformer T1 secondary at tap P7. (The low-side of the rectified output).
  • transfer sheets 70 are fed through chute 71 in registration with a toner image on the photoconductive belt 72.
  • the charge on the surface of the belt- 72 may be altered by an appropriately biased corotron 74 and- /or a pre-transfer lamp.
  • the transfer roller 75 and constant current bias source 76 are of the same design as that described in connection with FIG. 6.
  • an appropriate self-leveling layer 77 is a polyurethane material commercially available from the DuPont Company under the tradename Adiprine (Type L315) while examples of the relaxable layer 78 include materials such as the polyester urethanes.
  • An outer overcoating of low moisture permiability polymer material such as polyvinylidene chloride may be additionally applied.
  • the speed of the sheet through the nip 73 is about -20 inches per second.
  • the cleaning brush 80 with its associated vacuum housing 81 is positioned to clean stray toner and dirt from the outer surface of roller 75.
  • the corotron 82 in the post-nip area in FIG. 1, is commonly referred to as a detack corotron. It is designed to neutralize or lower the potential of the charge deposited onto the sheet 70 by transfer post-nip ionization. That is, corotron 82 is designed to neutralize most of the charge represented by the plus signs 30 in FIG. 6. Lowering the charge on the non-image areas of the transfer sheet makes the sheet easier to strip from the belt 72.
  • the output of the present constant current bias source 76 or 23 can be adjusted so that the tacking forceof the charge on the non-image side of sheet 70 does not tack the sheet 70 to the belt 72 too strongly.
  • the bias current previously described as I can be adjusted so that a detack corotron 82 is not necessary, although transfer efficiencymay be lowered.
  • Transport 83 includes the continuous belt 84 moving around roller 85 in the direction indicated. Acting through the bottom section of the belt 84 is a vacuum chamber 86 that pulls the sheet 70 to the bottom of the belt 84.
  • Transfer apparatus for accurately transferring .an image of electrically charged particles between an Original support and a transfer support comprising:
  • an original support for carrying the particles said support being electrically insulating at least in the absence of certain wavelengths of light;
  • a transfer electrode positioned adjacent said original support and said backing electrode to form pre-nip, nip, and post-nip regions and air gaps providing passage therethrough of said transfer support;
  • variable electrical bias means connected internally to said transfer electrode for providing current and variable voltage thereto for generating electrical fields between said backing and transfer electrodes in said pre-nip, nip and post-nip regions for transfer of said particles from said original support to said transfer support,
  • saidtransfer electrode including internal electrically relaxable means to provide asymmetricalexternal electrical field levels from said variable electrical bias means which are below substantial air ionization levels in said pre-nip region and substantially above air ionization levels at said post-nip regions,
  • variable electrical bias means comprising variable voltage applying means for regulating automatically said pre-nip, nip and post-nip field levels in response to changing electrical parameters affecting said fields by sensing and controlling the current applied to said transfer electrode from said electrical bias means.
  • variable electrical bias means is a constant current energy source.
  • said transfer electrode comprises a roller having an electrically conductive core connected to said bias means, and wherein said relaxable means is a thick layer of selectively resistive material around said core.
  • said transfer electrode further includes an electrically self-leveling layer comprising a thinner layer of substantially higher resistivity material than said relaxable layer overlying said relaxable layer.
  • charging apparatus for controlled air ionization charging of a moving surface to be charged, comprising:
  • a rotatable electrode roller positioned adjacent to said surface to be charged and defining at least one air gap therebetween'
  • variable electrical bias means internally connected to said roller electrode for applying current and variable voltage thereto for generating controlled air ionizing electrical fields in said air gap between said roller electrode and said surface to be charged;
  • roller electrode having a single conductive core to which said bias means is connected and a thick body of resistive material surrounding said core
  • said electrical bias means comprising variable voltage ization in said gap is controlled.

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  • General Physics & Mathematics (AREA)
  • Electrostatic Charge, Transfer And Separation In Electrography (AREA)
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BR (1) BR7308055D0 (ru)
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Cited By (92)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3860436A (en) * 1972-11-24 1975-01-14 Thomas Meagher Constant current biasing transfer system
US3861860A (en) * 1973-10-01 1975-01-21 Xerox Corp Dry fuser roll cleaning apparatus
US3861861A (en) * 1973-08-10 1975-01-21 Xerox Corp Fuser roll cleaning apparatus
US3870541A (en) * 1972-01-27 1975-03-11 Xerox Corp Selective transfer of an electrostatic toner image
US3879121A (en) * 1973-12-13 1975-04-22 Ibm Transfer system
US3884572A (en) * 1972-12-26 1975-05-20 Ibm Cleaning apparatus
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US6175711B1 (en) * 1998-10-16 2001-01-16 Fuji Xerox Co., Ltd. Image forming apparatus having a toner diffuser
US6269228B1 (en) * 1998-11-24 2001-07-31 Ricoh Company, Ltd. Method and apparatus for image forming performing improved cleaning and discharging operations on image forming associated members
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US20030118359A1 (en) * 2001-10-29 2003-06-26 Hiromi Ogiyama Transfer device for forming a stable transfer electric field, and an image forming apparatus including the transfer device
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US6680086B1 (en) 1998-07-08 2004-01-20 Mesto Paper Oy Method for making paper, assembly for implementing the method and paper product produced by the method
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JP2717574B2 (ja) * 1989-04-27 1998-02-18 キヤノン株式会社 画像形成装置

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US3870541A (en) * 1972-01-27 1975-03-11 Xerox Corp Selective transfer of an electrostatic toner image
US3860436A (en) * 1972-11-24 1975-01-14 Thomas Meagher Constant current biasing transfer system
US3884572A (en) * 1972-12-26 1975-05-20 Ibm Cleaning apparatus
US4172905A (en) * 1973-01-26 1979-10-30 The Commonwealth Of Australia Transferring xerographic images
US3960556A (en) * 1973-03-01 1976-06-01 Addressograph Multigraph Corporation Constant current toner transfer
US3861861A (en) * 1973-08-10 1975-01-21 Xerox Corp Fuser roll cleaning apparatus
US3861860A (en) * 1973-10-01 1975-01-21 Xerox Corp Dry fuser roll cleaning apparatus
US4023894A (en) * 1973-11-30 1977-05-17 Xerox Corporation Transfer apparatus
US3879121A (en) * 1973-12-13 1975-04-22 Ibm Transfer system
US4199356A (en) * 1974-02-01 1980-04-22 Mita Industrial Company Limited Electrophotographic process, of transferring a magnetic toner to a copy member having at least 3×1013 ohm-cm resistance
US3960109A (en) * 1974-04-01 1976-06-01 Addressograph Multigraph Corporation Electrostatic toner transfer
US3917881A (en) * 1974-04-01 1975-11-04 Addressograph Multigraph Electrostatic toner transfer
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US3920325A (en) * 1974-09-09 1975-11-18 Xerox Corp Moisture stable bias transfer roll
US4081212A (en) * 1974-11-18 1978-03-28 Oce-Van Der Grinten, N.V. System for electrostatically transferring powder images
US3935517A (en) * 1975-01-02 1976-01-27 Xerox Corporation Constant current charging device
US3954333A (en) * 1975-01-10 1976-05-04 Xerox Corporation Transfer roll having means for monitoring and controlling the resistivity thereof
US3954332A (en) * 1975-01-10 1976-05-04 Xerox Corporation Reproduction machine with improved transfer roll
US4183655A (en) * 1975-10-07 1980-01-15 Ricoh Company, Ltd. Cleaning means for image transfer unit in electrophotographic copying machines
US4110027A (en) * 1976-07-12 1978-08-29 Canon Kabushiki Kaisha Image transfer mechanism
US4338017A (en) * 1980-02-07 1982-07-06 Olympus Optical Company Limited Electrophotographic apparatus
US4309803A (en) * 1980-09-29 1982-01-12 Xerox Corporation Low cost foam roll for electrostatographic reproduction machine
US4371251A (en) * 1981-02-27 1983-02-01 Eastman Kodak Company Electrographic method and apparatus providing improved transfer of non-insulative toner
US4607935A (en) * 1984-04-18 1986-08-26 Eastman Kodak Company Roller transfer apparatus
US4796047A (en) * 1987-03-23 1989-01-03 Eastman Kodak Company Roller transfer apparatus having an extended nip exhibiting low pressure
US5168313A (en) * 1988-04-28 1992-12-01 Kabushiki Kaisha Toshiba Toner image transfer method and device for electrophotographic printing apparatus
US4977430A (en) * 1988-06-24 1990-12-11 Eastman Kodak Company Transfer roller power supply
US4998143A (en) * 1988-09-20 1991-03-05 Hitachi, Ltd. Electrophotographic image transfer member, electrophotographic image transfer device and electrophotographic recording apparatus
US5450180A (en) * 1988-11-02 1995-09-12 Canon Kabushiki Kaisha Image forming apparatus having constant current and voltage control in the charging and transfer regions
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US5119550A (en) * 1989-07-03 1992-06-09 Eastman Kodak Company Method of making transfer apparatus having vacuum holes
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US7214757B2 (en) 2000-03-09 2007-05-08 Eastman Kodak Company Polyurethane elastomers and shaped articles prepared therefrom
US6548154B1 (en) 2000-11-28 2003-04-15 Xerox Corporation Electrical charge relaxable wear resistant coating for bias charging or transfer member
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US7346287B2 (en) 2001-10-29 2008-03-18 Ricoh Company, Ltd. Transfer device for forming a stable transfer electric field, and an image forming apparatus including the transfer device
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US8396404B2 (en) 2010-08-26 2013-03-12 Xerox Corporation Image transfer nip method and apparatus using constant current controls
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Also Published As

Publication number Publication date
NL161899B (nl) 1979-10-15
FR2213519A1 (ru) 1974-08-02
DE2342856B2 (de) 1979-10-31
JPS5233494B2 (ru) 1977-08-29
NL7315343A (ru) 1974-05-28
DE2342856A1 (de) 1974-05-30
GB1448385A (en) 1976-09-08
DE2342856C3 (de) 1980-07-24
FR2213519B1 (ru) 1976-11-19
CA1030009A (en) 1978-04-25
JPS4984446A (ru) 1974-08-14
NL161899C (nl) 1980-03-17
BR7308055D0 (pt) 1974-10-22

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